CN114136805A - Metal sheet fracture strain determination method, storage medium and electronic device - Google Patents
Metal sheet fracture strain determination method, storage medium and electronic device Download PDFInfo
- Publication number
- CN114136805A CN114136805A CN202111273041.4A CN202111273041A CN114136805A CN 114136805 A CN114136805 A CN 114136805A CN 202111273041 A CN202111273041 A CN 202111273041A CN 114136805 A CN114136805 A CN 114136805A
- Authority
- CN
- China
- Prior art keywords
- sample plate
- strain
- bending
- determining
- bending angle
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 238000000034 method Methods 0.000 title claims abstract description 55
- 239000002184 metal Substances 0.000 title claims abstract description 23
- 238000005452 bending Methods 0.000 claims abstract description 181
- 238000012360 testing method Methods 0.000 claims abstract description 26
- 238000011056 performance test Methods 0.000 claims abstract description 11
- 239000000463 material Substances 0.000 claims description 21
- 239000003973 paint Substances 0.000 claims description 16
- 230000002829 reductive effect Effects 0.000 claims description 9
- 238000005507 spraying Methods 0.000 claims description 7
- 230000000875 corresponding effect Effects 0.000 description 47
- 229910000831 Steel Inorganic materials 0.000 description 26
- 239000010959 steel Substances 0.000 description 26
- 238000010586 diagram Methods 0.000 description 15
- 230000008569 process Effects 0.000 description 10
- 238000005259 measurement Methods 0.000 description 8
- 238000006073 displacement reaction Methods 0.000 description 6
- 238000000605 extraction Methods 0.000 description 4
- 230000006870 function Effects 0.000 description 4
- 238000003825 pressing Methods 0.000 description 4
- 238000011160 research Methods 0.000 description 4
- 238000004364 calculation method Methods 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 238000004590 computer program Methods 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000000284 extract Substances 0.000 description 2
- 238000005286 illumination Methods 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 230000036961 partial effect Effects 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000003672 processing method Methods 0.000 description 2
- 230000000750 progressive effect Effects 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 230000001360 synchronised effect Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000013075 data extraction Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 238000011326 mechanical measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 230000001502 supplementing effect Effects 0.000 description 1
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/20—Investigating strength properties of solid materials by application of mechanical stress by applying steady bending forces
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/60—Analysis of geometric attributes
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0023—Bending
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Health & Medical Sciences (AREA)
- Computer Vision & Pattern Recognition (AREA)
- Theoretical Computer Science (AREA)
- Geometry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
The invention discloses a method for determining fracture strain of a metal plate, which comprises the following steps: selecting a plurality of sample plates of the same type; recording an initial speckle image based on the digital image system; determining the average bending angle of the sample plate based on the extreme point cold bending performance test system; setting a plurality of different intermediate bending angles according to the average bending angle; sequentially bending the sample plate according to the magnitude sequence of each middle bending angle based on the extreme point cold bending performance test system, and recording the speckle images of the corresponding sample plate; determining strain values corresponding to the intermediate bending angles in DIC software based on the speckle images corresponding to the intermediate bending angles and the initial speckle images; determining strain values under the average bending angle of the sample plate based on the strain values corresponding to the middle bending angles; the fracture strain of the sample sheet is determined based on the strain value at the average bend angle. The implementation of the invention improves the accuracy of the test sample plate fracture strain.
Description
Technical Field
The invention relates to the technical field of mechanical measurement, in particular to a method for determining fracture strain of a metal plate, a storage medium and electronic equipment.
Background
With the rapid development of the automobile industry, advanced high-strength steel is applied to automobile body safety structural parts more and more by virtue of the advantages of high strength and toughness, and the problem of fracture failure caused by insufficient toughness is increasingly highlighted along with the improvement of material strength. In practical application scenarios, when an automobile collides, a structural member of the automobile body is mainly broken under plane bending. Therefore, the fracture strain under plane bending is an important index for characterizing the collision safety of automobiles. The toughness is generally evaluated internationally by means of the German automobile industry Association Standard VDA 238-100. The bending angle is a core index for evaluating the toughness of the steel plate in the industry, and the size of the bending angle is positively correlated with the level of the toughness of the steel plate. However, the magnitude of the bending angle can only be used as an index for the transverse direction comparing the toughness of the steel plate, and cannot be used for characterizing the fracture limit of the material in a finite element. At present, a simple method capable of accurately representing the fracture limit of a steel plate under plane strain is lacked.
Disclosure of Invention
In order to solve the technical problem, the invention provides a method for determining the fracture strain of a metal plate, which is applied to a limit tip cold bending performance testing system and a digital image system, wherein the limit tip cold bending performance testing system comprises: at least two rollers and a pressure head; the two rollers are arranged in an axisymmetric mode by taking the loading edge of the pressure head as an axis, and the rollers are used for bearing a sample plate; the pressure head is used for applying a vertical force to the sample plate to enable the sample plate to generate a bending angle; the digital image system is used for extracting strain data of the sample plate;
the method comprises the following steps:
selecting a plurality of sample plates of the same type according to a preset rule;
sequentially spraying white paint and black paint on the upper surfaces of the sample plates;
recording an initial speckle image of an upper surface of a sample plate based on the digital image system;
determining an average bending angle of the sample plate based on the extreme point cold bending performance test system;
setting a plurality of different intermediate bending angles according to the average bending angle, wherein the plurality of different intermediate bending angles are all smaller than the average bending angle;
sequentially bending the sample plate according to the magnitude sequence of each middle bending angle based on the extreme sharp cold bending performance test system, and recording a speckle image of the sample plate corresponding to each middle bending angle based on a digital image system;
determining strain values corresponding to the intermediate bending angles based on the speckle images corresponding to the intermediate bending angles and the initial speckle images;
determining strain values under the average bending angle of the sample plate based on the strain values corresponding to the intermediate bending angles;
determining a fracture strain of the sample sheet based on the strain value at the average bend angle.
Further, the selecting a plurality of sample plates of the same type according to a preset rule includes:
the tensile strength of the selected sample plate is greater than 980MPa, the thickness of the sample plate is 1.0-2.0 mm, the width of the sample plate is 15-60 mm, and the length of the sample plate is 40-60 mm.
Further, the determining an average bending angle of the sample plate material based on the extreme point cold bending performance testing system comprises:
adjusting the distance between rollers on two sides of the pressure head according to the thickness of the sample plate;
selecting a target sample plate from the plurality of sample plates of the same type;
placing the target sample plate on the roller, and applying a downward pressure to the target sample plate at a constant speed based on the pressure head to bend the target sample plate until the bending load force of the target sample plate is reduced to a preset threshold value or the target sample plate has visible cracks, and recording the bending angle of the target sample plate;
repeatedly executing: selecting a target sample plate from the plurality of sample plates of the same type;
placing the target sample plate on the roller, and applying a downward pressure to the target sample plate at a constant speed based on the pressure head to bend the target sample plate until the bending load force of the target sample plate is reduced to a preset threshold value or the target sample plate has visible cracks, and recording the bending angle of the target sample plate until the number of the bending angles of the target sample plate meets a preset number requirement;
determining an average bend angle of the sample sheet material based on the bend angles of all of the target sample sheet materials.
Further, the sample plate is sequentially bent according to the magnitude sequence of the middle bending angles based on the extreme point cold bending performance testing system, and the method comprises the following steps:
determining a downward movement distance of the pressure head corresponding to each intermediate bending angle based on each intermediate bending angle;
and sequentially controlling the downward movement of the pressure heads based on the magnitude sequence of the downward movement distance of each pressure head, so that the sample plate is bent to a corresponding middle bending angle.
Further, determining a strain value corresponding to each intermediate bending angle based on the speckle image corresponding to each intermediate bending angle and the initial speckle image comprises:
selecting a target image point with maximum strain in the speckle image corresponding to each intermediate bending angle according to the initial speckle image;
selecting a rectangular frame with the width of 0.4-1mm and the length of the difference value between the length of the sample plate and a preset width threshold value in the speckle image corresponding to each middle bending angle by taking a line which passes through the target image point and is parallel to the pressure head as an axis;
and comparing all image points in the rectangular frame with corresponding image points in the initial speckle image to determine strain values corresponding to the intermediate bending angles.
Further, determining a strain value at an average bending angle of the sample sheet material based on the strain values corresponding to the respective intermediate bending angles includes:
and fitting the strain values corresponding to the intermediate bending angles into a strain curve, and intercepting the strain value corresponding to the average bending angle on an extension line of the strain curve.
Further, the breaking strain of the sample plate is determined according to the following formula, including:
wherein epsilon1Is the value of strain at the average bend angle,
is the strain at break of the sample panel.
Further, the average bend angle is 32 to 102 degrees.
In another aspect, the present invention provides a computer-readable storage medium, in which at least one instruction or at least one program is stored, and the at least one instruction or the at least one program is loaded and executed by a processor to implement the method for determining fracture strain of a metal plate material as described above.
In another aspect, the present invention provides an electronic device comprising at least one processor, and a memory communicatively coupled to the at least one processor; the memory stores instructions executable by the at least one processor, and the at least one processor implements the method for determining the fracture strain of the metal sheet by executing the instructions stored in the memory.
According to the method for determining the fracture strain of the metal plate, the storage medium and the electronic equipment, provided by the invention, on the premise of not changing a limit sharp cold bending performance test system, a discontinuous loading and unloading method is adopted, and by means of a digital image system, high-strength steel strain measurement can be carried out in an off-line mode, so that the accuracy of the strain measurement is ensured, and the equipment cost is saved.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings used in the description of the embodiment or the prior art will be briefly described below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
FIG. 1 is a schematic structural diagram illustrating a limit tip cold bending performance testing system according to an embodiment of the present application;
FIG. 2 is a schematic diagram of a digital image system according to an embodiment of the present application;
FIG. 3 is a schematic flow chart diagram illustrating a method for determining fracture strain of a metal sheet according to an embodiment of the present disclosure;
FIG. 4 is a schematic diagram of an extreme tip cooling corner measurement provided by an embodiment of the present application;
FIG. 5 is a diagram illustrating strain calculated in DIC software for speckle images corresponding to bend angles according to embodiments of the present application;
FIG. 6 is a schematic diagram of a cloud (for strain calculation) in DIC software for each of the intermediate bend angles provided by an embodiment of the present application;
fig. 7 is a schematic diagram of a strain numerical fitting curve corresponding to each of the intermediate bending angles provided in the embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, apparatus, article, or device that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or device.
Fig. 1 is a schematic structural diagram of a limit tip cold bending performance testing system according to an embodiment of the present application, and as shown in fig. 1, the limit tip cold bending performance testing system may include at least two rollers and a press head, where the two rollers are disposed axially symmetrically with respect to a loading edge of the press head, and the rollers are used for bearing a sample plate; the indenter is used for applying a vertical force to the sample plate to enable the sample plate to generate a bending angle, and it can be understood that the indenter can apply a downward acting force F to the sample plate from top to bottom.
Fig. 2 is a schematic structural diagram of a digital image system according to an embodiment of the present disclosure, and as shown in fig. 2, the digital image system may include a computer, an image capture card, a CCD (camera), and an illumination light source, where the computer and the image capture card may be loaded with DIC software for extracting strain data in a captured speckle image, the CCD (camera) is used for capturing the speckle image of a sample plate, and the illumination light source is used for supplementing light to the sample plate when capturing the image. The basic principle of the digital image system can be understood as that the displacement vector of the same pixel point in two speckle images before and after the deformation of the object surface is tracked (or matched) to obtain the strain value.
The method for determining the fracture strain of the metal plate provided by the invention can be applied to the extreme point cold bending performance test system and the digital image system, can realize an accurate characterization means of the fracture strain of the steel plate under the VDA238-100 standard and a corresponding data processing method, stably and accurately extracts and analyzes strain data, and provides technical support for finite element simulation of engineering technicians in the whole vehicle collision process, specifically, as shown in FIG. 3, FIG. 3 is a flow schematic diagram of the method for determining the fracture strain of the metal plate shown according to the embodiment of the application, and the method can comprise the following steps:
s102, selecting a plurality of sample plates of the same type according to a preset rule.
In practical applications, different strain at break characterizes different fracture toughness, and the predetermined rule indicated herein may be a steel plate for an automobile (sample plate) having a tensile strength of more than 980MPa and a sample plate thickness of between 1.0 and 2.0 mm.
Specifically, for better measurement of the breaking strain of the sample plate, the size of the breaking strain may be defined, for example, the sample plate has a thickness of 1.0 to 2.0mm, a width of 15mm to 60mm, and a length of 40mm to 60 mm.
In an alternative embodiment, the sample sheet material tensile strength may be greater than 1180 MPa.
In an alternative embodiment, the width of the specimen ranges from 30 to 60 mm.
In an alternative embodiment, the specimen has a thickness of 1.2-1.8 mm.
And S104, spraying white paint and black paint on the upper surfaces of the sample plates in sequence.
Specifically, as shown in fig. 1, the upper surface of the sample plate may be a surface on a side close to the indenter in the extreme point cold bending performance test system. When determining the fracture strain of the metal plate, white paint and black paint can be sprayed on the upper surface of the sample plate in advance. The white paint and the black paint are sprayed to improve the imaging effect of the speckle images of the digital image system.
It can be understood that the specific spraying can use white paint as primer, after the white paint is uniformly sprayed, black paint is sprayed, the black paint is used for spraying fine and uniform spots on the white paint, and when DIC experiment is carried out, the computer and the image acquisition card can calculate the corresponding strain value by identifying the change among the spots in different deformation stages;
wiping a sample plate, measuring the thickness and the distance between the slit ends in two directions, spraying a thin layer of white matte paint on the surface photographed by DIC, and spraying uniformly distributed black speckles after thorough drying for strain measurement
And S106, recording an initial speckle image of the upper surface of the sample plate based on the digital image system.
And S108, determining the average bending angle of the sample plate based on the limit sharp cold bending performance test system.
In a specific implementation, the determining an average bending angle of the sample plate based on the extreme point cold bending performance testing system includes:
adjusting the distance between rollers on two sides of the pressure head according to the thickness of the sample plate;
it can be understood that the distance between the rollers on the two sides of the pressure head in the extreme point cold bending performance testing system is related to the thickness of the sample plate, and when the extreme point cold bending performance testing system is used for bending the sample plate, the distance L between the rollers can be adjusted to be 2t +0.5mm according to the VDA238-100 standard, wherein t is the thickness of the sample plate, and sample plates with different thicknesses correspond to different distances L between the rollers.
Selecting a target sample plate from the plurality of sample plates of the same type.
And placing the target sample plate on the roller, and applying a downward pressure to the target sample plate at a constant speed based on the pressure head to bend the target sample plate until the bending load force of the target sample plate is reduced to a preset threshold value or the target sample plate has visible cracks, and recording the bending angle of the target sample plate.
Repeatedly executing: selecting a target sample plate from the plurality of sample plates of the same type;
placing the target sample plate on the roller, and applying a downward pressure to the target sample plate at a constant speed based on the pressure head to bend the target sample plate until the bending load force of the target sample plate is reduced to a preset threshold value or the target sample plate has visible cracks, and recording the bending angle of the target sample plate until the number of the bending angles of the target sample plate meets a preset number requirement;
determining an average bend angle of the sample sheet material based on the bend angles of all of the target sample sheet materials.
Specifically, the preset number is not specifically limited in the embodiments of the present specification, and may be set according to actual needs. The bending load force-displacement curve load force can be understood as a peak value, and the extreme point cold bending performance test system can automatically extract the peak value.
Illustratively, 3 to 5 target sample plates can be selected from the plurality of sample plates, the indenter is pressed at a loading rate of 20mm/min according to the VDA238-100 standard, and the sample plates can be stopped when the bending load force-displacement curve of the sample plates is reduced to about 10% of the peak value or when the sample plates have visible cracks. Then, the maximum average bending angle, the minimum average bending angle and the average bending angle of 3-5 target sample plate materials are calculated according to the formula in the VDA238-100 standard.
It is understood that the average bend angle may be determined based on the bend angles corresponding to 3-5 target sample sheets.
It is noted that the average bend angle of the sample sheet material is guaranteed to be between 32 and 102 to ensure that the method is effective.
S108, setting a plurality of different middle bending angles according to the average bending angle, wherein the plurality of different middle bending angles are all smaller than the average bending angle.
In practical applications, in order to better measure the breaking strain of the sample plate, a plurality of different intermediate bending angles can be set according to the average bending angle of the sample plate.
For example, a plating-free hot-formed steel (sample plate) of 1.7GPa grade and 2.0mm thickness produced by a steel mill is selected, and a pattern of 30-60mm is selected. It was confirmed that the average bending angle of the plating-free hot-formed steel was 55 °, the intermediate bending angles were 0 °,10 °, 20 °, 30 °, 35 °, 40 °, 45 °, and 50 °.
And S110, sequentially bending the sample plate according to the magnitude sequence of the middle bending angles based on the extreme point cold bending performance testing system, and recording the speckle image of the sample plate corresponding to each middle bending angle based on a digital image system.
Specifically, the sequentially bending the sample plate according to the magnitude sequence of the intermediate bending angles based on the extreme point cold bending performance testing system may include:
determining a downward movement distance of the pressure head corresponding to each intermediate bending angle based on each intermediate bending angle;
and sequentially controlling the downward movement of the pressure heads based on the magnitude sequence of the downward movement distance of each pressure head, so that the sample plate is bent to a corresponding middle bending angle.
Specifically, as shown in fig. 4, the downward movement distance of the indenter can be calculated as follows. Wherein the pressure head is that the tip does:
wherein,
is the middle bending angle, p is the distance from the pressure head to the roller on one side, c is the distance from the center of the pressure head to the center of the roller, SThe sample plate is bent to the downward moving distance corresponding to the middle bending angle,
radius of the roller, t0The thickness of the sample plate, r, is the radius of the indenter.
In practical application, after each middle bending angle is determined, the downward moving distance of the pressure head corresponding to each middle bending angle can be calculated through the formula, and then the downward moving of the pressure head is sequentially controlled according to the magnitude sequence of the downward moving distance of the pressure head, so that the sample plate corresponding to the middle bending angle is obtained.
Specifically, after setting a plurality of different intermediate bending angles, 1 sample plate may be selected for the intermittent test. Converting the displacement corresponding to different angles of the sample plate with different thicknesses according to a formula in a VDA238-100 standard, namely: pressing the sample plate by 20 degrees by adjusting the pressing displacement, unloading, recording the unloaded angle of the sample plate, arranging the sample plates as shown in figure 1, and recording the speckle image of the sample plate corresponding to each middle bending angle; pressing the original sample plate to 30 degrees, unloading, recording the unloaded angle of the sample plate, arranging the sample plates as shown in figure 1, and recording the speckle image of the sample plate corresponding to each middle bending angle; according to the steps, the sample plate is pressed to 30 degrees, then the sample plate is pressed once at intervals of 5-10 degrees, and the test is stopped until the load force on the bending load force-displacement curve of the sample plate is reduced to a preset threshold value or the target sample plate has visible cracks. In order to ensure the accuracy of the measurement, 2 to 4 sample plates can be selected again, and the steps are repeated.
And S112, determining strain values corresponding to the intermediate bending angles based on the speckle images corresponding to the intermediate bending angles and the initial speckle images.
Specifically, the determining the strain value corresponding to each intermediate bending angle based on the speckle image corresponding to each intermediate bending angle and the initial speckle image includes:
selecting a target image point with maximum strain in the speckle image corresponding to each intermediate bending angle according to the initial speckle image;
selecting a rectangular frame with the width of 0.4-1mm and the length of the difference value between the length of the sample plate and a preset width threshold value in the speckle image corresponding to each middle bending angle by taking a line which passes through the target image point and is parallel to the pressure head as an axis;
and comparing all image points in the rectangular frame with corresponding image points in the initial speckle image to determine strain values corresponding to the intermediate bending angles.
In the specific implementation process, the computer and DIC software in the image acquisition card can find the target image point with the maximum strain in the corresponding speckle image, draw a frame with the width of 0.4-1.0mm and the length between the width minus 0.5mm of the sample plate and the width 50% of the sample plate on the middle cross section by taking the target image point as an axis, and calculate the main strain values epsilon corresponding to different middle bending angles in the DIC software according to the corresponding initial speckle image1. Specifically, the rectangular frame can be referred to as a rectangular frame drawn by a white dotted line in fig. 5.
The wider the width of the rectangular frame is selected, the larger the range of the patterns participating in calculation is, and the smaller the maximum strain value obtained in the way is. In order to avoid the occurrence of large deviation caused by selecting only the maximum value, in this embodiment, a width range of a rectangular frame is defined, and the strain is calculated in this range to obtain the difference between the maximum value and the minimum value of the strain value, and the width range or the standard deviation of the rectangular frame is generally within 5%; thus, the three-point sharp cold bending strain at break can be selected within a range, the upper and lower limits of which are within 5%.
The applicant finds through a large number of experimental studies that points cannot be selected (the maximum point strain may be related to sample processing, and partial errors also exist in the in-plane bending, so that the maximum point cannot be directly used, the maximum point strain is easy to be larger, and the deviation of different samples is large), or lines are simply drawn, and in order to ensure the stability, the range of the selected picture frame is selected; the objective is to achieve strain in the sub-range with a final standard deviation within 5%. In addition, above 30 °, it is recommended to select one data point every 5 ° intervals, if the intervals are too small, the data points are dense, the experiment is difficult to control accurately, if the intervals are too large, the data point collection is insufficient, the finally obtained strain is increased along with the sample fluctuation, and the stability of the data is difficult to control, therefore, above 30 °, it is recommended to select one data point every 5 ° intervals.
S114, determining strain values under the average bending angle of the sample plate material based on the strain values corresponding to the intermediate bending angles,
specifically, determining the strain value at the average bending angle of the sample plate material based on the strain values corresponding to the intermediate bending angles includes:
and fitting the strain values corresponding to the intermediate bending angles into a strain curve, and intercepting the strain value corresponding to the average bending angle on an extension line of the strain curve.
The method can be ensured to be effective only by ensuring that the average bending angle of the steel plate is between 32 and 102 degrees. When the average bending angle is less than 32 degrees, 3 complete angle-strain data between 20 degrees and (the average maximum bending angle is minus 2-6 degrees) cannot be guaranteed, if only two data exist, the error of the fitted curve is too large, and the method cannot be adopted; when the average bending angle of the steel plate is larger than 102 degrees, the steel plate has very good fracture toughness, on one hand, the equipment is damaged due to the fact that the pressing distance of a punch is too large in the three-point sharp cold bending process of a sample exceeding 102 degrees, on the other hand, the problem of DIC data identification in the plane exists due to the fact that the bending angle of the sample is too large, namely, data cannot be identified and extracted, and therefore data accuracy cannot be guaranteed. In addition, research has shown that the toughness is better for the material with low strength grade, and research has shown that, for the material with 590MPa grade, when the bending angle is larger than 100 °, the situation that the load begins to drop without cracking of the sample may occur, which will definitely affect the measurement of strain and the judgment of material fracture failure. It is worth noting that according to the previous experimental research aiming at a large amount of industrial high-strength steel by the applicant, in order to ensure the accuracy of the test, the technology only aims at the material with the tensile strength of more than 980 MPa.
And S116, determining the fracture strain of the sample plate based on the strain value under the average bending angle.
Specifically, the breaking strain of the sample plate may be determined according to the following formula, including:
wherein epsilon1Is the value of the principal strain at the average bend angle,
is the strain at break of the sample panel.
As described above, the method for determining the fracture strain of the metal plate provided by the invention has the following beneficial effects: the invention provides a plane strain test characterization means, which is characterized in that on the premise of not changing conventional three-point-tip cold bending test equipment, a discontinuous loading and unloading method is adopted, and high-strength steel strain measurement is carried out in an off-line mode by means of DIC equipment, so that on one hand, the investment of high-precision equipment is avoided, the test cost of the fracture strain is reduced, and meanwhile, the cheapness of the fracture strain test is ensured; meanwhile, a corresponding data processing method is provided, a reasonable extraction method is obtained aiming at the strain extraction of the high-strength steel through a large amount of experimental research, the finally obtained strain difference value is ensured to be within a range of 5% when the data extraction is carried out within the recommended extraction strain range, the accurate data calibration is ensured, and a stable data source is provided for the subsequent finite element simulation.
For a better explanation of the invention, the experimental data for different sample panels calculated using the above method are as follows:
example 1: selecting a plating-free hot forming steel with the thickness of 2.0mm and the grade of 1.7GPa produced by a certain steel factory, selecting a 30 x 60mm sample, wherein the average bending angle is 55 degrees, and the middle bending angles are respectively 0 degree, 10 degrees, 20 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees and 50 degrees
The following figures are examples, strain clouds (speckle images) of a sample at different bending stages are drawn by using DIC software, as shown in fig. 6, fig. 6 is a schematic diagram of a speckle image of a strain value corresponding to each intermediate bending angle provided by the embodiment of the present application;
strain extraction: finding the maximum strain point in the software, drawing a 0.5mm wide and 28mm long box on the middle cross section by taking the point as an axis to count the strains under different processes, and extracting the main strain epsilon1A strain value of;
fitting the strain data of 30-50 degrees (according to the sample condition) obtained by a method of 0.5mm width by using a linear fitting method, and intercepting the strain value under the average bending angle of the material on an extension line of a fitting curve, as shown in FIG. 7;
to ensure test stability, the strain obtained in a 0.5mm wide process was repeated three times, and the strain was averaged and then calculated according to the formula
Converted to fracture strain.
The strain at break was calculated to be 0.341.
Example 2: a 1.5GPa grade, 1.8mm thick 22MnB5 hot formed steel from a steel mill was selected, a 30 x 60mm pattern was selected, the average bend angle was 56 °, the intermediate bend angles were 20 °, 30 °, 35 °, 40 °, 45 °, 50 °, respectively, and the calculated strain at break was 0.352.
Example 3: a 1.5GPa grade, 1.4mm thick 22MnB5 hot formed steel from a steel mill was selected, a 30 x 60mm pattern was selected, the average bend angle was 59 °, the intermediate bend angles were 20 °, 30 °, 35 °, 40 °, 45 °, 50 °, respectively, and the calculated strain at break was 0.348.
Example 4: QP1500 (strength 1500MPa) of 1.4mm thickness produced by a certain steel mill was selected, 60X 60mm patterns were selected, the average bending angle was 73 degrees, the intermediate bending angles were 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, respectively, and the calculated strain at break was 0.375.
Example 5: a steel mill-produced TBF1470 (strength 1500MPa) of 1.4mm thickness was selected, a 60 x 60mm pattern was selected, the average bending angle was 66 °, the intermediate bending angles were 20 °, 30 °, 40 °, 50 °, 60 °, respectively, and the calculated strain at break was 0.358.
Example 6: a steel mill with a thickness of 1.4mm DP980 (strength 980MPa) was selected, a 60 x 60mm design was selected, the average bend angle was 84 °, the intermediate bend angles were 20 °, 30 °, 40 °, 50 °, 60 °, 70 °, 80 °, and the calculated strain at break was 0.465.
The above functions, if implemented in the form of software functional units and sold or used as a separate product, may be stored in a computer-readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention.
The embodiment of the present invention further provides a storage medium, where at least one instruction, at least one program, a code set, or an instruction set is stored in the storage medium, and the at least one instruction, the at least one program, the code set, or the instruction set may be executed by a processor of an electronic device to implement the method for determining a fracture strain of a metal plate described above.
Optionally, in an embodiment of the present invention, the storage medium may include, but is not limited to: various media capable of storing program codes, such as a usb disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic disk, or an optical disk.
It should be noted that: the precedence order of the above embodiments of the present invention is only for description, and does not represent the merits of the embodiments. And specific embodiments thereof have been described above. Other embodiments are within the scope of the following claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some embodiments, multitasking and parallel processing may also be possible or may be advantageous.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in the embodiments provided herein may include non-volatile and/or volatile memory, among others. Non-volatile memory can include read-only memory (ROM), Programmable ROM (PROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), Dynamic RAM (DRAM), Synchronous DRAM (SDRAM), Double Data Rate SDRAM (DDRSDRAM), Enhanced SDRAM (ESDRAM), Synchronous Link DRAM (SLDRAM), Rambus Direct RAM (RDRAM), direct bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, as for the apparatus, the electronic device and the storage medium embodiment, since they are substantially similar to the method embodiment, the description is relatively simple, and the relevant points can be referred to the partial description of the method embodiment.
It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program instructing relevant hardware, where the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.
It should be noted that, in the present specification, the embodiments are all described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments may be referred to each other. The implementation principle and the generated technical effect of the testing method provided by the embodiment of the invention are the same as those of the system embodiment, and for the sake of brief description, the corresponding contents in the system embodiment can be referred to where the method embodiment is not mentioned.
In the several embodiments provided in the present application, it should be understood that the disclosed system and method may be implemented in other ways. The apparatus embodiments described above are merely illustrative, and for example, the flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
Finally, it should be noted that: the above-mentioned embodiments are only specific embodiments of the present invention, which are used for illustrating the technical solutions of the present invention and not for limiting the same, and the protection scope of the present invention is not limited thereto, although the present invention is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the embodiments of the present invention, and they should be construed as being included therein. Therefore, the protection scope of the present invention shall be subject to the protection scope of the above claims.
Claims (9)
1. A method for determining the fracture strain of a metal plate is applied to a limit tip cold bending performance testing system and a digital image system, and the limit tip cold bending performance testing system comprises the following steps: at least two rollers and a pressure head; the two rollers are arranged in an axisymmetric mode by taking the loading edge of the pressure head as an axis, and the rollers are used for bearing a sample plate; the pressure head is used for applying a vertical force to the sample plate to enable the sample plate to generate a bending angle; the digital image system is used for extracting strain data of the sample plate;
the method comprises the following steps:
selecting a plurality of sample plates of the same type according to a preset rule;
sequentially spraying white paint and black paint on the upper surfaces of the sample plates;
recording an initial speckle image of an upper surface of a sample plate based on the digital image system;
determining an average bending angle of the sample plate based on the extreme point cold bending performance test system;
setting a plurality of different intermediate bending angles according to the average bending angle, wherein the plurality of different intermediate bending angles are all smaller than the average bending angle;
sequentially bending the sample plate according to the magnitude sequence of each middle bending angle based on the extreme sharp cold bending performance test system, and recording a speckle image of the sample plate corresponding to each middle bending angle based on a digital image system;
determining strain values corresponding to the intermediate bending angles based on the speckle images corresponding to the intermediate bending angles and the initial speckle images;
determining strain values under the average bending angle of the sample plate based on the strain values corresponding to the intermediate bending angles;
determining a fracture strain of the sample sheet based on the strain value at the average bend angle; the breaking strain of the sample sheet is determined according to the following formula, including:
wherein epsilon1Is the value of strain at the average bend angle,
is the strain at break of the sample panel.
2. The method for determining the fracture strain of the metal plate according to claim 1, wherein the step of selecting a plurality of sample plates of the same type according to a preset rule comprises the steps of:
the tensile strength of the selected sample plate is greater than 980MPa, the thickness of the sample plate is 1.0-2.0 mm, the width of the sample plate is 15-60 mm, and the length of the sample plate is 40-60 mm.
3. The method of determining the fracture strain of the metal sheet according to claim 1, wherein the determining the average bending angle of the sample sheet based on the extreme point cold bending performance testing system comprises:
adjusting the distance between rollers on two sides of the pressure head according to the thickness of the sample plate;
selecting a target sample plate from the plurality of sample plates of the same type;
placing the target sample plate on the roller, and applying a downward pressure to the target sample plate at a constant speed based on the pressure head to bend the target sample plate until the bending load force of the target sample plate is reduced to a preset threshold value or the target sample plate has visible cracks, and recording the bending angle of the target sample plate;
repeatedly executing: selecting a target sample plate from the plurality of sample plates of the same type;
placing the target sample plate on the roller, and applying a downward pressure to the target sample plate at a constant speed based on the pressure head to bend the target sample plate until the bending load force of the target sample plate is reduced to a preset threshold value or the target sample plate has visible cracks, and recording the bending angle of the target sample plate until the number of the bending angles of the target sample plate meets a preset number requirement;
determining an average bend angle of the sample sheet material based on the bend angles of all of the target sample sheet materials.
4. The method for determining the breaking strain of the metal sheet according to claim 1, wherein the step of bending the sample sheet sequentially according to the magnitude sequence of the intermediate bending angles based on the extreme point cold bending performance testing system comprises the steps of:
determining a downward movement distance of the pressure head corresponding to each intermediate bending angle based on each intermediate bending angle;
and sequentially controlling the downward movement of the pressure heads based on the magnitude sequence of the downward movement distance of each pressure head, so that the sample plate is bent to a corresponding middle bending angle.
5. The method for determining the fracture strain of the metal sheet according to claim 1, wherein determining the strain value corresponding to each intermediate bending angle based on the speckle image corresponding to each intermediate bending angle and the initial speckle image comprises:
selecting a target image point with maximum strain in the speckle image corresponding to each intermediate bending angle according to the initial speckle image;
selecting a rectangular frame with the width of 0.4-1mm and the length of the difference value between the length of the sample plate and a preset width threshold value in the speckle image corresponding to each middle bending angle by taking a line which passes through the target image point and is parallel to the pressure head as an axis;
and comparing all image points in the rectangular frame with corresponding image points in the initial speckle image to determine strain values corresponding to the intermediate bending angles.
6. The method for determining the fracture strain of the metal sheet according to claim 1, wherein determining the strain value at the average bending angle of the sample sheet based on the strain values corresponding to the respective intermediate bending angles comprises:
and fitting the strain values corresponding to the intermediate bending angles into a strain curve, and intercepting the strain value corresponding to the average bending angle on an extension line of the strain curve.
7. The method of determining the strain at break of a metal sheet as set forth in claim 1, wherein the average bending angle is 32 to 102 degrees.
8. A computer readable storage medium having stored therein at least one instruction or at least one program, the at least one instruction or the at least one program being loaded and executed by a processor to implement the method of determining the fracture strain of a metal sheet according to any one of claims 1 to 7.
9. An electronic device comprising at least one processor, and a memory communicatively coupled to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the at least one processor implements the method of determining sheet metal fracture strain as set forth in any one of claims 1-7 by executing the instructions stored by the memory.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111273041.4A CN114136805A (en) | 2021-10-29 | 2021-10-29 | Metal sheet fracture strain determination method, storage medium and electronic device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111273041.4A CN114136805A (en) | 2021-10-29 | 2021-10-29 | Metal sheet fracture strain determination method, storage medium and electronic device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN114136805A true CN114136805A (en) | 2022-03-04 |
Family
ID=80395081
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202111273041.4A Pending CN114136805A (en) | 2021-10-29 | 2021-10-29 | Metal sheet fracture strain determination method, storage medium and electronic device |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN114136805A (en) |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007198895A (en) * | 2006-01-26 | 2007-08-09 | Kobe Steel Ltd | Evaluation method of delayed breaking resistance of high-strength steel sheet |
| US20160161382A1 (en) * | 2013-06-26 | 2016-06-09 | Nippon Steel & Sumitomo Metal Corporation | Metal sheet bending fracture determination method and recording medium |
| CN111307612A (en) * | 2020-03-12 | 2020-06-19 | 中国汽车工程研究院股份有限公司 | Method for testing hydrogen-induced delayed fracture performance of ultrahigh-strength automobile steel plate |
| CN113340732A (en) * | 2021-05-31 | 2021-09-03 | 北京理工大学 | Heterogeneous material multi-parameter inversion method and device based on automatic image partitioning |
| CN113466066A (en) * | 2021-06-30 | 2021-10-01 | 山东大学 | DIC technology-based method for measuring fatigue deformation and crack width of concrete material |
-
2021
- 2021-10-29 CN CN202111273041.4A patent/CN114136805A/en active Pending
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007198895A (en) * | 2006-01-26 | 2007-08-09 | Kobe Steel Ltd | Evaluation method of delayed breaking resistance of high-strength steel sheet |
| US20160161382A1 (en) * | 2013-06-26 | 2016-06-09 | Nippon Steel & Sumitomo Metal Corporation | Metal sheet bending fracture determination method and recording medium |
| CN111307612A (en) * | 2020-03-12 | 2020-06-19 | 中国汽车工程研究院股份有限公司 | Method for testing hydrogen-induced delayed fracture performance of ultrahigh-strength automobile steel plate |
| CN113340732A (en) * | 2021-05-31 | 2021-09-03 | 北京理工大学 | Heterogeneous material multi-parameter inversion method and device based on automatic image partitioning |
| CN113466066A (en) * | 2021-06-30 | 2021-10-01 | 山东大学 | DIC technology-based method for measuring fatigue deformation and crack width of concrete material |
Non-Patent Citations (1)
| Title |
|---|
| H.L. CAI ET AL.: "A Simple Methodology to Determine Fracture Strain of Press-Hardened Steels Under Plane Strain Bending", METALLURGICAL AND MATERIALS TRANSACTIONS A * |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Chen et al. | The evaluation of formability of the 3rd generation advanced high strength steels QP980 based on digital image correlation method | |
| CN110779797B (en) | Method for measuring plastic strain ratio in metal tensile test process | |
| JP6958521B2 (en) | Stress-strain relationship estimation method | |
| CN110740821B (en) | Method for evaluating deformation limit of metal plate on sheared surface, method for predicting crack, and method for designing press die | |
| Zang et al. | Measurements of Bauschinger effect and transient behavior of a quenched and partitioned advanced high strength steel | |
| Dziallach et al. | Sheet metal testing and flow curve determination under multiaxial conditions | |
| Kurz et al. | Press-hardening of zinc coated steel-characterization of a new material for a new process | |
| JP2020134348A (en) | Stress-strain relation estimation method | |
| Pham et al. | Twisting analysis of ultra-thin metallic sheets | |
| Gothivarekar et al. | Advanced FE model validation of cold-forming process using DIC: Air bending of high strength steel | |
| Van der Aa et al. | An experimental and numerical study of the wall ironing process of polymer coated sheet metal | |
| Song et al. | Investigation of various necking criteria for sheet metal formability analysis using digital image strain data | |
| JP5098901B2 (en) | Calculation method of material property parameters | |
| CN114136805A (en) | Metal sheet fracture strain determination method, storage medium and electronic device | |
| Liewald et al. | Surface roughening of an aluminum 6016 alloy during bending and hemming | |
| Sangkharat et al. | Using image processing on Erichsen cup test machine to calculate anisotropic property of sheet metal | |
| Zhang et al. | Formability evaluation of sheet metals based on global strain distribution | |
| KR101358282B1 (en) | A contactlessly diagnosing device for analyzing formed shapes and cracks of sheet metal for test and a software for it | |
| RU2333471C2 (en) | Punch-device for testing and method of testing of sheet material for springback and capacity at double-angle bending (versions) | |
| WO2022123825A1 (en) | Method for calculating residual stress | |
| RU2359243C2 (en) | Die instrument for sheet metal testing for spring back and critical parametres at three-point bending (versions) | |
| Abvabi et al. | Development of an inverse routine to predict residual stresses in the material based on a bending test | |
| CN111948041A (en) | Method for determining elastic-plastic transition boundary line of high-speed tensile plate-shaped sample | |
| Longo et al. | Control system algorithm for the prediction of sprinback in air bending | |
| RU2308697C1 (en) | Method of testing sheet material |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| RJ01 | Rejection of invention patent application after publication |
Application publication date: 20220304 |
|
| RJ01 | Rejection of invention patent application after publication |